A human leukemic cell line has been used to study steroid actions. Glucocorticoids stop these cells in the G1 phase of the cell cycle, after which they die. Steroid resistant subclones have been isolated and are being analyzed. HTC cell variants have been found to lack coordinate control over 5 steroid-sensitive functions. Lack of estrogen receptor in human breast cancer has been found to correlate with high response rate to chemotherapy. Sezary syndrome cells have been found to contain glucocorticoid receptors, as have lines of mouse lymphomas bearing specific sets of Ly antigens. The pre-activated and activated forms of glucorticoid receptors have been separated and factors influencing activation studied. Affinity labels for glucocorticoid receptors are being developed. Chromosome mapping of certain steroid-related functions has begun. Studies of prolactin mRNA have been developed.